NGL20
About
The GNSS solution named ’NGL20’ is produced by the Nevada Geodetic Laboratory (NGL) using a Precise Point Positioning (PPP) data analysis strategy. The latest version of GipsyX software and models, orbits and clocks from the Jet Propulsion Laboratory (JPL) have been used to produce daily position time series expressed in the ITRF2020 reference frame (Blewitt et al. 2018). The data set covers the period January 1996 to September 2025.
The Sixteenth session of the Group of Experts for the Global Sea Level Observing System (GLOSS), held in Busan (Republic of Korea), 11-13 April 2019, tasked the SONEL data assembly centre to consider including the NGL solution (position time series and velocities) for the subset of GNSS stations nearby tide gauges. Among the more than 23,000 stations processed by NGL, as many as 1523 have actually been identified as co-located, or nearby, tide gauges, and/or capable of measuring sea leavel through the GNSS-Reflectometry technique.
The GNSS velocities, provided here for 1195 stations (nearby tide gauges and reference frame stations included) with a minimum record length of 3 years and data gaps not exceeding 30%, are produced by NGL using the MIDAS estimator (Blewitt et al. 2016).
More details about the GNSS data analysis strategy can be found here or in Blewitt et al. (2016).
Citation
For the time series:
Blewitt G., W. C. Hammond, C. Kreemer (2018). Harnessing the GPS data explosion for interdisciplinary science. Eos, 99, doi:10.1029/2018EO104623.
For the velocities:
Blewitt G., C. Kreemer, W.C. Hammond, J. Gazeaux (2016). MIDAS robust trend estimator for accurate GPS station velocities without step detection. Journal of Geophysical Research, 121, 2054-2068, doi:10.1002/2015JB012552.
Download
– Vertical velocities table
The NGL20_Vertical-Velocities_Table provides the vertical GPS velocities and uncertainties from the 1195 stations fulfilling the criteria of 3 years of minimum length and data gaps not exceeding 30%, estimated by the NGL group using MIDAS (Blewitt et al. 2016).
– Daily time series
The NGL20.zip file contains individual station data files of the 1523 daily position time series in ITRF2020 with respect to the position at the mid time series epoch. These positions are expressed in meters in the local frame (North, East, and Up). The reference position and the 3D velocity (obtained using MIDAS) in the local coordinate system (East, North, Up) are provided in the header of each file.
– Position discontinuities
The NGL20_discontinuities_Table.txt file provides the position offsets that can affect the station position and velocity estimates, as indicated by the NGL group. Note that MIDAS should be robust regarding the velocity estimates in presence of offsets, but not the parametric methods (e.g. least squares adjustment).
More information and data sets useful for other applications can be found at the Nevada Geodetic Laboratory website.
